Aircraft fuel tanks include a number of sections that are secured together with fasteners. The fasteners and the mating surfaces of the tanks are coated with a sealant to ensure that the fuel tanks do not leak. The sealant also forms a mechanical barrier between the fuel in the tanks and electrical arcing that may arise between the fasteners and the sections of the fuel tank if the aircraft is struck by lightning. However, the electrical arcing that may occur during a lightning strike may generate a mechanical stress on the sealant, which may cause the sealant to crack or break, enabling an arc to ignite the fuel. Therefore, the Federal Aviation Administration (FAA) requires that testing be performed to ensure that the sealants used in aircraft fuel tanks are capable of withstanding the stress due to lightning strikes on the aircraft.
Current testing methods for aircraft fuel tanks include assembling a sample of the fasteners and panels used for a fuel tank, and applying a high current through the sample. The current generates arcing around the fasteners, which stresses the sealant applied to the fasteners. The samples are then inspected to determine if breaks or cracks in the sealant are present around the fasteners.
The problem with the current testing method is that assembling the sample is expensive and time consuming. Further, it is difficult to reliably reproduce the electrical arcing around the fasteners from one sample to another, or from one fastener to another in the same sample, due to variations in the mechanical interface between the fasteners and the panels.
Therefore, there is a desire to improve the testing of how sealants utilized for aircraft fuel tanks may respond to lightning strikes upon the aircraft.